Chemotherapeutic research will be continued on special problems pertaining to new and clinically established antitumor agents. The studies will be based on previous laboratory findings and clinical interest. Systems employed in these investigations will include established murine tumor systems, induced and spontaneous tumors and animal and human tumors growing in athymic mice. Structure-activity studies will be extended to additional classes of active agents. In relation to clinical interest in multiple drug therapy, emphasis will be placed on further investigation of combination chemotherapy. Investigations of combined-modality approaches to cancer treatment will continue. Studies will be continued on underlying principles involved in chemotherapeutic approaches. Specific problems arising in the clinical use of drugs will continue to be investigated. Emphasis will be placed on international collaborative research effort in relation to new antitumor drugs and treatment modalities.